// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/base64url.h"

#include <stddef.h>

#include "base/base64.h"
#include "base/macros.h"
#include "base/numerics/safe_math.h"
#include "base/strings/string_util.h"
#include "third_party/modp_b64/modp_b64.h"

namespace base {

const char kPaddingChar = '=';

// Base64url maps {+, /} to {-, _} in order for the encoded content to be safe
// to use in a URL. These characters will be translated by this implementation.
const char kBase64Chars[] = "+/";
const char kBase64UrlSafeChars[] = "-_";

void Base64UrlEncode(const StringPiece& input,
    Base64UrlEncodePolicy policy,
    std::string* output)
{
    Base64Encode(input, output);

    ReplaceChars(*output, "+", "-", output);
    ReplaceChars(*output, "/", "_", output);

    switch (policy) {
    case Base64UrlEncodePolicy::INCLUDE_PADDING:
        // The padding included in |*output| will not be amended.
        break;
    case Base64UrlEncodePolicy::OMIT_PADDING:
        // The padding included in |*output| will be removed.
        const size_t last_non_padding_pos = output->find_last_not_of(kPaddingChar);
        if (last_non_padding_pos != std::string::npos)
            output->resize(last_non_padding_pos + 1);

        break;
    }
}

bool Base64UrlDecode(const StringPiece& input,
    Base64UrlDecodePolicy policy,
    std::string* output)
{
    // Characters outside of the base64url alphabet are disallowed, which includes
    // the {+, /} characters found in the conventional base64 alphabet.
    if (input.find_first_of(kBase64Chars) != std::string::npos)
        return false;

    const size_t required_padding_characters = input.size() % 4;
    const bool needs_replacement = input.find_first_of(kBase64UrlSafeChars) != std::string::npos;

    switch (policy) {
    case Base64UrlDecodePolicy::REQUIRE_PADDING:
        // Fail if the required padding is not included in |input|.
        if (required_padding_characters > 0)
            return false;
        break;
    case Base64UrlDecodePolicy::IGNORE_PADDING:
        // Missing padding will be silently appended.
        break;
    case Base64UrlDecodePolicy::DISALLOW_PADDING:
        // Fail if padding characters are included in |input|.
        if (input.find_first_of(kPaddingChar) != std::string::npos)
            return false;
        break;
    }

    // If the string either needs replacement of URL-safe characters to normal
    // base64 ones, or additional padding, a copy of |input| needs to be made in
    // order to make these adjustments without side effects.
    if (required_padding_characters > 0 || needs_replacement) {
        std::string base64_input;

        CheckedNumeric<size_t> base64_input_size = input.size();
        if (required_padding_characters > 0)
            base64_input_size += 4 - required_padding_characters;

        base64_input.reserve(base64_input_size.ValueOrDie());
        input.AppendToString(&base64_input);

        // Substitute the base64url URL-safe characters to their base64 equivalents.
        ReplaceChars(base64_input, "-", "+", &base64_input);
        ReplaceChars(base64_input, "_", "/", &base64_input);

        // Append the necessary padding characters.
        base64_input.resize(base64_input_size.ValueOrDie(), '=');

        return Base64Decode(base64_input, output);
    }

    return Base64Decode(input, output);
}

} // namespace base
